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1

Seismic Wave Velocities in Deep Sediments in Poland: Borehole and Refraction Data Compilation

Polkowski M., Grad M.

Acta Geophysica

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2015

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Vol. 63, no. 3

698--714

EN

Sedimentary cover has significant influence on seismic wave travel times and knowing its structure is of great importance for studying deeper structures of the Earth. Seismic tomography is one of the methods that require good knowledge of seismic velocities in sediments and unfortunately by itself cannot provide detailed information about distribution of seismic velocities in sedimentary cover. This paper presents results of P-wave velocity analysis in the old Paleozoic sediments in area of Polish Lowland, Folded Area, and all sediments in complicated area of the Carpathian Mountains in Poland. Due to location on conjunction of three major tectonic units - the Precambrian East European Craton, the Paleozoic Platform of Central and Western Europe, and the Alpine orogen represented by the Carpathian Mountains the maximum depth of these sediments reaches up to 25 000 m in the Carpathian Mountains. Seismic velocities based on 492 deep boreholes with vertical seismic profiling and a total of 741 vertical seismic profiles taken from 29 seismic refraction profiles are analyzed separately for 14 geologically different units. For each unit, velocity versus depth relations are approximated by second or third order polynomials.

2

The role of reflected wave in tomographic velocity interpretation of model WSP data

Kasina Z.

Acta Geophysica Polonica

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1999

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Vol. 47, nr 4

401-409

EN

Initial evaluation has been undertaken for improving tomographic images in vertical seismic profiling (VSP) by utilization, in addition to direct wave, the reflected wave as well. This evaluation has been performed basing on model computations. The input data in tomographic inversion have been traveltimes generated using ray tracing with curved rays for selected seismogeological medium models. It was proved that when we use traveltimes of wave reflected from the reflector in the bottom of transmission medium we can considerably improve the range of medium coverage with seismic rays and create a possibility to define much more precisely the location of velocity heterogeneities during tomographic inversion.

3

Analysis of a seismic record in the frequency-wavenumber domain

Ismal M. A.

Acta Geophysica Polonica

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1998

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Vol. 46, nr 3

325-350

EN

Multi-domain frequency-wavenumber (F-K) filtering has been developed to reduce the complex coherent noise and to solve problems inherent in the application of F-K filtering to down-dipseismic data that can occur in both land and marine data. The noises can be classified into coherent and uncoherent, multiples, ground roll and acoustic waves. The Fast Fourier Transform (FFT) is used two times to segregate a seismic record into two different half planes of frequency-wavenumber space (F-K) on the travelling direction of the events. The computation of both forward and inverse 2-D FFT is done to eliminate the unwanted waves. The F-K plots are periodic in both F and K with filters that are symmetric with respect to K only, in wchich the 2-D F-K spectrum is folded about the F-axis. Apparent-velocity filters can also be designed to remove a noise wedge rather than to pass a signal wedge, with a filter called 'butterfly'. For ideal processing, fine spatial sampling during the original recording is required. The aliasing noise is obviously clearer at shallower depths than deeper and at nearer offsets than at father ones. This technique is appplied to separate the upgoing and downgoig events of the Vertical Seismic Profiling (VSP), wanted and unwanted events of the VSP and surface seismics, and to enhance the signal-to-high velocity noise ratio. Three field examples were selected from varying locations to explain how the F-K processing ma be used.